Tower with tensioning cables

ABSTRACT

A tower, which may be used for a wind turbine, is provided. The tower includes at least one concrete tower section having a plurality of tensioning cables. The tensioning cables are configured to induce a compressive force on the concrete tower section. The tensioning cables are spaced from an exterior surface of the concrete tower section by a substantially uniform distance.

BACKGROUND OF THE INVENTION

This invention relates generally to towers. In particular, but notlimited thereto, the present invention relates to wind turbine towershaving tensioning cables.

Recently, wind turbines have received increased attention asenvironmentally safe and relatively inexpensive alternative energysources. With this growing interest, considerable efforts have been madeto develop wind turbines that are reliable and efficient.

Generally, a wind turbine includes a rotor having multiple blades. Therotor is mounted to a housing or nacelle, which is positioned on top ofa truss or tubular tower. Utility grade wind turbines (i.e., windturbines designed to provide electrical power to a utility grid) canhave large rotors (e.g., 30 or more meters in diameter). Blades on theserotors transform wind energy into a rotational torque or force thatdrives one or more generators that may be rotationally coupled to therotor through a gearbox. The gearbox steps up the inherently lowrotational speed of the turbine rotor for the generator to efficientlyconvert mechanical energy to electrical energy, which is fed into autility grid.

Several technical installations require a tower or a mast to which theinstallation is mounted. Non-limiting examples of such installations arewind turbines, antenna towers used in broadcasting or mobiletelecommunication, pylons used in bridge work, or power poles.Typically, the tower is made of steel and must be connected to afoundation made of reinforced concrete. In these cases, the typicaltechnical solution is to provide a large, solid reinforced concretefoundation at the bottom of the tower. In typical applications the towerfoundation extends about 12 meters below the ground level, and can beabout 18 meters or more in diameter.

In larger utility grade wind turbines (e.g., 2.5 MW or more) it is oftendesired to have towers with heights of 80 meters or more. The higher hubheights provided by larger towers enable the wind turbine's rotor toexist in higher mean wind speed areas, and this results in increasedenergy production. Increases in tower height invariably have lead tocorresponding increases in the mass, length and diameter of the tower.However, it becomes difficult to construct and transport large windturbine towers as the local transportation infrastructure (e.g., roads,bridges, vehicles, etc.) often impose limits on the length, weight anddiameter of tower components.

BRIEF DESCRIPTION OF THE INVENTION

According to one aspect of the present invention, a tower is provided.The tower includes at least one concrete tower section having aplurality of tensioning cables. The tensioning cables are configured toinduce a compressive force on the concrete tower section. The tensioningcables are spaced from an exterior surface of the concrete tower sectionby a substantially uniform distance.

According to another aspect of the present invention, a wind turbinetower is provided. The tower includes at least one concrete towersection having a plurality of tensioning cables. The tensioning cablesare configured to induce a compressive force on the concrete towersection. The tensioning cables are spaced from an exterior surface ofthe concrete tower section by a substantially uniform distance.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates a wind turbine to which the aspects of the presentinvention can be applied;

FIG. 2 illustrates a side view of a wind turbine and wind turbine tower,according to an aspect of the present invention;

FIG. 3 illustrates a side view of a concrete tower section, according toan aspect of the present invention;

FIG. 4 illustrates a cut-away, perspective view of a portion of a windturbine tower, according to an aspect of the present invention;

FIG. 5 illustrates a side view of a wind turbine tower, according to anaspect of the present invention;

FIG. 6 illustrates a side view of a concrete tower section incorporatinggrooves in the outer wall thereof, according to an aspect of the presentinvention;

FIG. 7 illustrates a top view of a concrete tower section, according toan aspect of the present invention;

FIG. 8 illustrates a top view of a concrete tower section having acover, according to an aspect of the present invention;

FIG. 9 illustrates a partial perspective view of a portion of a concretetower section with the cover as shown in FIG. 8, according to an aspectof the present invention

DETAILED DESCRIPTION OF THE INVENTION

Reference will now be made in detail to the various aspects of theinvention, one or more examples of which are illustrated in the figures.Each example is provided by way of explanation of the invention, and isnot meant as a limitation of the invention. For example, featuresillustrated or described as part of one aspect can be used on or inconjunction with other aspects to yield yet a further aspect. It isintended that the present invention includes such modifications andvariations.

FIG. 1 shows a wind turbine to which the aspects of the presentinvention can be advantageously applied. However, it should beunderstood that the present invention is not limited or restricted towind turbines but can also be applied to tower structures used in othertechnical fields. In particular, the various aspects of the presentinvention may also be applied to antenna towers used in broadcasting ormobile telecommunication or to pylons used in bridge work. Therefore,although the aspects of the invention will be exemplified with referenceto a wind turbine, the scope of the present invention shall not belimited thereto.

The wind turbine 100 shown in FIG. 1 comprises a tower 110 bearing anacelle 120 on its top end. A rotor including a rotor hub 130 and rotorblades 140 is attached to one side of the nacelle 120. The tower 110 ismounted on a foundation 150. The tower may be formed of rolled steel andhave multiple stacked sections 112 (e.g., about three or four mainsections). Alternatively, the tower 120 may be formed of a truss-likestructure and/or may have a cylindrical or tapered profile. Typically,the tower foundation 150 is made of a solid mass of reinforced concrete.

It would be advantageous to increase tower height in order to capturemore energy due to higher mean wind speeds. An aspect of the presentinvention provides a tower or tower section fabricated from concrete. Aconcrete base section can be used to elevate a conventional rolled-steeltower, or the entire tower can be formed of concrete. Concrete isdefined as a mixture of aggregates and binder or any suitable masonrysupport. As one non-limiting example only, the aggregates may be sandand gravel or crushed stone, and the binder may be water and cement.

While concrete is strong in compression, it is weak in tension. Steel isstrong under forces of tension, so combining the two elements results inthe creation of very strong concrete components. In conventionalreinforced concrete, the high tensile strength of steel is combined withconcrete's great compressive strength to form a structural material thatis strong in both compression and tension. The principle behindprestressed concrete is that compressive stresses induced byhigh-strength steel tendons in a concrete member before loads areapplied will balance the tensile stresses imposed in the member duringservice.

Compressive stresses can be induced in prestressed concrete either bypretensioning or post-tensioning the steel reinforcement. Inpretensioning, the steel is stretched before the concrete is placed.High-strength steel tendons or cables are placed between two abutmentsand stretched to a portion of their ultimate strength. Concrete ispoured into molds around the tendons/cables and allowed to cure. Oncethe concrete reaches the required strength, the stretching forces arereleased. As the steel reacts to regain its original length, the tensilestresses are translated into a compressive stress in the concrete.

In post-tensioning, the steel or cable is stretched after the concretehardens. Concrete is cast in the desired shape first. Once the concretehas hardened to the required strength, the steel tendons or cables areattached and stretched against the ends of the unit and anchored offexternally, placing the concrete into compression. According to anaspect of the present invention, post-tensioned concrete is used forwind turbine towers or wind turbine tower sections.

FIG. 2 illustrates a wind turbine tower, in a partially exploded view,according to an aspect of the present invention. The wind turbine 200includes a tower 210 which may include one or more sections 112. Thetower sections 112 may be formed of rolled steel. A concrete towersection 215 is located at the bottom of the tower and supports the uppersections 112. The concrete tower section 215 includes concrete walls 260which may be formed in one or more sections and have a tapered (asshown) or cylindrical shape. Alternatively, the tower sections 210and/or 215 can have any desired cross-section, such as but not limitedto, oval, rectangular, polygonal, etc. One or more anchor plates 270 aresecured to the top of the concrete walls 260. The anchor plates 270 canextend radially outward past the upper outer edge of walls 260. Aplurality of tensioning cables 280 are secured at one end to the anchorplates 270, and at the other end to foundation 250.

The tensioning cables 280 are located circumferentially around andexternal to the concrete walls 260, and are positioned close to and at asubstantially uniform distance from an outer or exterior surface ofconcrete walls 260. The term “substantially uniform” can be defined ashaving approximately the same, or having a slightly varying distance(e.g., a slight taper). In other words, the tensioning cables 280 can beparallel to or nearly parallel to the outer surface of concrete walls260. As one non-limiting example only, the tensioning cables 280 may bespaced from an exterior surface of a top portion of concrete wall 260 byabout two inches, whereas the cables 280 may be spaced from an exteriorsurface of a bottom portion of concrete wall 260 by about six inches.The cables 280 can be of the post-tensioned type, and they apply acompressive force to concrete walls 260. The use of external cablesresults in a larger moment arm and lower cable forces, and eventually,smaller cables would be required when compared to using the cablesinternal to the concrete segments. In other aspects of the invention,the tensioning cables 280 are positioned close to an exterior surface ofconcrete walls 260, but may be configured to have a slightly increasingor slightly decreasing distance from the exterior surface of concretewalls 260.

During operation of the wind turbine 200, wind flows in the directionindicated by arrow 202. The force of the wind creates a load on the windturbine and tower. The up-wind side of the tower (i.e., the left side ofthe tower as shown in FIG. 2) would be under tension, while thedown-wind side of the tower (i.e., the right side of the tower as shownin FIG. 2) would be under compression. As discussed previously, concreteperforms very well under compression. However, concrete does not performas well under tension. The tensioning cables 280 help to counteract thewind caused forces of tension on the tower section 215.

One advantage provided by the present invention is the reduction of theeffective moment-arm on tower section 215. By positioning the tensioningcables 280 close to and external to the exterior surface of concretewalls 280 the tower 210, 215 reduces its effective moment-arm to provideresistance to wind loads. This invention moves the cables outside, butin close proximity to the tower walls. For example, a very smalldiameter tower having internal cables would need thicker walls andthicker cables to counteract the forces applied by the wind, whencompared to a larger diameter tower having external cables. The largerdiameter tower could be made with thinner concrete walls and havesmaller diameter cables when compared to the very small diameter tower.

FIG. 3 illustrates a side view of concrete tower section 215. Tensioningcables 280 are affixed at one end to anchor plate(s) 270, and at theother end to foundation 250. The anchor plate 270 is attached (e.g., bybolts or fasteners) to the top of the concrete tower 260, and a portionof the anchor plate 270 protrudes outboard beyond the outer diameter ofthe top of concrete tower 260. The tensioning cables 280 are attached tothe anchor plate 270 at the overhanging portion of the anchor plate. Theanchor plate 270 can be made in multiple segments (e.g., three or foursections) that substantially cover the top of concrete walls 260. Theanchor plate 270 may also have holes (not shown) through which theflange attachment bolts are embedded into the concrete wall 260. Thesecan be used to attach the upper potion of the concrete wall 260 toconventional steel tube tower sections 112. At the bottom end, thecables are secured/attached into the foundation.

FIG. 4 illustrates a partial perspective view of a portion of a windturbine tower according to an aspect of the present invention. Anoptional adapter section 405 may be used between a concrete towersection 260 and an upper tower section 112. In one example, the adaptersection could be formed of concrete and/or steel, and the upper towersection 112 may be formed of rolled steel. The anchor plate 270 acts asan attachment point for tensioning cables 280 and the flange 113 ofupper tower section 112. The flange can be attached to the anchor plate270 with any suitable fastening arrangement (e.g., a nut, washer andbolt system). The tensioning cables 280 may also be attached to theanchor plate in a similar fashion and may have threaded ends designed toaccept a washer and nut.

FIG. 5 illustrates a side view of a wind turbine tower 500 havingmultiple concrete tower sections 260, 361, 362. The second concretetower section 361 is attached via anchor plate 270 or via a flange (notshown) to bottom section 260. Tensioning cables 381 are placedcircumferentially around the exterior surface of concrete tower section361, and are attached to anchor plates 270 and 371. The third concretetower section 362 is attached via anchor plate 371 or via a flange (notshown) to second concrete tower section 361. Tensioning cables 382 areplaced circumferentially around the exterior surface of concrete towersection 362, and are attached to anchor plate 371 and anchor plate 372.Alternatively, the individual tensioning cables 280, 381, 382 may bereplaced by ling individual cables running from the foundation 250 tothe top anchor plate 372. As discussed previously, upper concrete towersections 361 and 362 could be replaced with one or more steel towersections. The upper steel tower sections would not require thetensioning cables 381 and 382.

In another aspect of the present invention, FIG. 6 illustrates a sideview of a concrete tower section 615 having external grooves 690 inwhich the tensioning cables 680 can reside. This configuration helps tocenter the cable loads in the body of the concrete wall 660, thusensuring a more uniform compressive load in the concrete wall 660. Thisconfiguration may also reduce the occurrence of tensile loads in theconcrete wall 660.

FIG. 7 illustrates a view from the top down of concrete tower section615. The concrete wall 660 and the grooves 690 formed therein are shownin phantom. The anchor plate 670 can be configured to overhang the outerportions of concrete wall 660 or the anchor plate 670 may have its outerdiameter aligned (as shown) or approximately flush with the outerdiameter of wall 660. The anchor plate 670 can be attached to concretewall 660 via bolts 672 or any other suitable fastener or fastenerarrangement.

FIG. 8 illustrates a top down view of another aspect of the presentinvention. A removable, non-structural or semi-structural cover 810 canbe incorporated on the outside of the concrete tower section 615,covering both the tensioning cables 680 and the concrete wall 660. Thecover 810 can be made of plastic, composite, sheet metal or any othersuitable fabric or material. The cover 810 may be comprised of one ormore sections, and may have one or more seams. The seams could bearranged vertically, horizontally and/or any direction therebetween. Thecover 810 can also provide protection (e.g., from the weather,vandalism, etc.) for the tensioning cables 680 and or the concrete wall660. FIG. 9 illustrates a partial perspective view of the concrete towersection 615 during installation of cover 810.

The grooves 690 in concrete wall 660 provide several advantages, a fewof which are, (1) protecting the external tensioning cables 680 (evenmore so with cover 810), (2) keeps the cables 680 away from view (i.e.,reduces visual impact), (3) allows for easy maintenance of the cables680 by facilitating external access, and (4) centers the compressiveload on the concrete (due to the post-tensioned cables 680) in the bodyof the concrete wall 660.

While the invention has been described in terms of various specificembodiments, those skilled in the art will recognize that the inventioncan be practiced with modification within the spirit and scope of theclaims.

1. A tower comprising: at least one concrete tower section having aplurality of tensioning cables, the plurality of tensioning cablesconfigured to induce a compressive force on the at least one concretetower section; wherein each of the plurality of tensioning cables arespaced from an exterior surface of the at least one concrete towersection by a substantially uniform distance.
 2. The tower of claim 1,further comprising: at least one anchor plate attached to a top portionof the at least one concrete tower section; wherein each of theplurality of tensioning cables are attached to the at least one anchorplate.
 3. The tower of claim 2, wherein each of the plurality oftensioning cables are attached to a foundation of the tower.
 4. Thetower of claim 1, further comprising: one or more upper tower sections;an adapter section located between the at least one concrete towersection and the one or more upper tower sections; at least one anchorplate attached to at least one of the one or more upper tower sections;wherein each of the plurality of tensioning cables are attached to theat least one anchor plate.
 5. The tower of claim 4, wherein each of theplurality of tensioning cables are attached to a foundation of thetower.
 6. The tower of claim 1, further comprising: at least one uppertower section attached to the at least one concrete tower section. 7.The tower of claim 6, wherein the at least one upper tower section iscomprised of rolled steel.
 8. The tower of claim 1, the at least oneconcrete tower section further comprising: a plurality of groovesdisposed in an exterior surface of the at least one concrete towersection; wherein each of the plurality of tensioning cables arecontained substantially within each of the plurality of grooves.
 9. Thetower of claim 8, further comprising: at least one cover configured tobe attached to the tower; wherein the plurality of tensioning cableswithin the plurality of grooves are substantially covered by the atleast one cover.
 10. The tower of claim 1, wherein each of the pluralityof tensioning cables are configured to be closer to a top exteriorsurface of the at least one concrete tower section than to a bottomexterior surface of the at least one concrete tower section.
 11. A windturbine tower, comprising: at least one concrete tower section having aplurality of tensioning cables, the plurality of tensioning cablesconfigured to induce a compressive force on the at least one concretetower section; wherein each of the plurality of tensioning cables arespaced from an exterior surface of the at least one concrete towersection by a substantially uniform distance.
 12. The wind turbine towerof claim 11, further comprising: at least one anchor plate attached to atop portion of the at least one concrete tower section; wherein each ofthe plurality of tensioning cables are attached to the at least oneanchor plate.
 13. The wind turbine tower of claim 12, wherein each ofthe plurality of tensioning cables are also attached to a foundation ofthe wind turbine tower.
 14. The wind turbine tower of claim 11, furthercomprising: one or more upper tower sections; an adapter section locatedbetween the at least one concrete tower section and the one or moreupper tower sections; at least one anchor plate attached to at least oneof the one or more upper tower sections; wherein each of the pluralityof tensioning cables are attached to the at least one anchor plate. 15.The wind turbine tower of claim 14, wherein each of the plurality oftensioning cables are attached to a foundation of the wind turbinetower.
 16. The wind turbine tower of claim 11, further comprising: atleast one upper tower section attached to the at least one concretetower section.
 17. The wind turbine tower of claim 16, wherein at leastone upper tower section is comprised of rolled steel.
 18. The windturbine tower of claim 11, the at least one concrete tower sectionfurther comprising: a plurality of grooves disposed in an exteriorsurface of the at least one concrete tower section; wherein each of theplurality of tensioning cables are contained substantially within theplurality of grooves.
 19. The wind turbine tower of claim 18, furthercomprising: at least one cover configured to be attached to the windturbine tower; wherein the plurality of tensioning cables within theplurality of grooves are covered by the at least one cover.
 20. The windturbine tower of claim 11, wherein each of the plurality of tensioningcables are configured to be closer to a top exterior surface of the atleast one concrete tower section than to a bottom exterior surface ofthe at least one concrete tower section.